package t5750.derby;

import java.sql.*;
import java.util.ArrayList;
import java.util.Properties;

/**
 * <p>
 * This sample program is a minimal Java application showing JDBC access to a
 * Derby database.
 * </p>
 * <p>
 * Instructions for how to run this program are given in <A
 * HREF=example.html>example.html</A>, by default located in the same directory
 * as this source file ($DERBY_HOME/demo/programs/simple/).
 * </p>
 * <p>
 * Derby applications can run against Derby running in an embedded or a
 * client/server framework.
 * </p>
 * <p>
 * When Derby runs in an embedded framework, the JDBC application and Derby run
 * in the same Java Virtual Machine (JVM). The application starts up the Derby
 * engine.
 * </p>
 * <p>
 * When Derby runs in a client/server framework, the application runs in a
 * different JVM from Derby. The connectivity framework (in this case the Derby
 * Network Server) provides network connections. The client driver is loaded
 * automatically.
 * </p>
 */
public class SimpleApp {
	/* the default framework is embedded */
	private String framework = "embedded";
	private String protocol = "jdbc:derby:";

	/**
	 * <p>
	 * Starts the demo by creating a new instance of this class and running the
	 * <code>go()</code> method.
	 * </p>
	 * <p>
	 * When you run this application, you may give one of the following
	 * arguments:
	 * <ul>
	 * <li><code>embedded</code> - default, if none specified. Will use Derby's
	 * embedded driver. This driver is included in the derby.jar file.</li>
	 * <li><code>derbyclient</code> - will use the Derby client driver to access
	 * the Derby Network Server. This driver is included in the derbyclient.jar
	 * file.</li>
	 * </ul>
	 * <p>
	 * When you are using a client/server framework, the network server must
	 * already be running when trying to obtain client connections to Derby.
	 * This demo program will will try to connect to a network server on this
	 * host (the localhost), see the <code>protocol</code> instance variable.
	 * </p>
	 * <p>
	 * When running this demo, you must include the correct driver in the
	 * classpath of the JVM. See <a href="example.html">example.html</a> for
	 * details.
	 * </p>
	 * 
	 * @param args
	 *            This program accepts one optional argument specifying which
	 *            connection framework (JDBC driver) to use (see above). The
	 *            default is to use the embedded JDBC driver.
	 */
	public static void main(String[] args) {
		new SimpleApp().go(args);
		System.out.println("SimpleApp finished");
	}

	/**
	 * <p>
	 * Starts the actual demo activities. This includes creating a database by
	 * making a connection to Derby (automatically loading the driver), creating
	 * a table in the database, and inserting, updating and retrieving some
	 * data. Some of the retrieved data is then verified (compared) against the
	 * expected results. Finally, the table is deleted and, if the embedded
	 * framework is used, the database is shut down.
	 * </p>
	 * <p>
	 * Generally, when using a client/server framework, other clients may be (or
	 * want to be) connected to the database, so you should be careful about
	 * doing shutdown unless you know that no one else needs to access the
	 * database until it is rebooted. That is why this demo will not shut down
	 * the database unless it is running Derby embedded.
	 * </p>
	 *
	 * @param args
	 *            - Optional argument specifying which framework or JDBC driver
	 *            to use to connect to Derby. Default is the embedded framework,
	 *            see the <code>main()</code> method for details.
	 * @see #main(String[])
	 */
	void go(String[] args) {
		/* parse the arguments to determine which framework is desired */
		parseArguments(args);
		System.out.println("SimpleApp starting in " + framework + " mode");
		/*
		 * We will be using Statement and PreparedStatement objects for
		 * executing SQL. These objects, as well as Connections and ResultSets,
		 * are resources that should be released explicitly after use, hence the
		 * try-catch-finally pattern used below. We are storing the Statement
		 * and Prepared statement object references in an array list for
		 * convenience.
		 */
		Connection conn = null;
		// list of Statements, PreparedStatements
		ArrayList<Statement> statements = new ArrayList<Statement>();
		PreparedStatement psInsert;
		PreparedStatement psUpdate;
		Statement s;
		ResultSet rs = null;
		try {
			Properties props = new Properties(); // connection properties
			// providing a user name and password is optional in the embedded
			// and derbyclient frameworks
			props.put("user", "user1");
			props.put("password", "user1");
			/*
			 * By default, the schema APP will be used when no username is
			 * provided. Otherwise, the schema name is the same as the user name
			 * (in this case "user1" or USER1.)
			 * 
			 * Note that user authentication is off by default, meaning that any
			 * user can connect to your database using any password. To enable
			 * authentication, see the Derby Developer's Guide.
			 */
			String dbName = "derbyDB"; // the name of the database
			/*
			 * This connection specifies create=true in the connection URL to
			 * cause the database to be created when connecting for the first
			 * time. To remove the database, remove the directory derbyDB (the
			 * same as the database name) and its contents.
			 * 
			 * The directory derbyDB will be created under the directory that
			 * the system property derby.system.home points to, or the current
			 * directory (user.dir) if derby.system.home is not set.
			 */
			conn = DriverManager.getConnection(protocol + dbName
					+ ";create=true", props);
			System.out.println("Connected to and created database " + dbName);
			// We want to control transactions manually. Autocommit is on by
			// default in JDBC.
			conn.setAutoCommit(false);
			/*
			 * Creating a statement object that we can use for running various
			 * SQL statements commands against the database.
			 */
			s = conn.createStatement();
			statements.add(s);
			// We create a table...
			s.execute("create table location(num int, addr varchar(40))");
			System.out.println("Created table location");
			// and add a few rows...
			/*
			 * It is recommended to use PreparedStatements when you are
			 * repeating execution of an SQL statement. PreparedStatements also
			 * allows you to parameterize variables. By using PreparedStatements
			 * you may increase performance (because the Derby engine does not
			 * have to recompile the SQL statement each time it is executed) and
			 * improve security (because of Java type checking).
			 */
			// parameter 1 is num (int), parameter 2 is addr (varchar)
			psInsert = conn
					.prepareStatement("insert into location values (?, ?)");
			statements.add(psInsert);
			psInsert.setInt(1, 1956);
			psInsert.setString(2, "Webster St.");
			psInsert.executeUpdate();
			System.out.println("Inserted 1956 Webster");
			psInsert.setInt(1, 1910);
			psInsert.setString(2, "Union St.");
			psInsert.executeUpdate();
			System.out.println("Inserted 1910 Union");
			// Let's update some rows as well...
			// parameter 1 and 3 are num (int), parameter 2 is addr (varchar)
			psUpdate = conn
					.prepareStatement("update location set num=?, addr=? where num=?");
			statements.add(psUpdate);
			psUpdate.setInt(1, 180);
			psUpdate.setString(2, "Grand Ave.");
			psUpdate.setInt(3, 1956);
			psUpdate.executeUpdate();
			System.out.println("Updated 1956 Webster to 180 Grand");
			psUpdate.setInt(1, 300);
			psUpdate.setString(2, "Lakeshore Ave.");
			psUpdate.setInt(3, 180);
			psUpdate.executeUpdate();
			System.out.println("Updated 180 Grand to 300 Lakeshore");
			/*
			 * We select the rows and verify the results.
			 */
			rs = s.executeQuery("SELECT num, addr FROM location ORDER BY num");
			/*
			 * we expect the first returned column to be an integer (num), and
			 * second to be a String (addr). Rows are sorted by street number
			 * (num).
			 * 
			 * Normally, it is best to use a pattern of while(rs.next()) { // do
			 * something with the result set } to process all returned rows, but
			 * we are only expecting two rows this time, and want the
			 * verification code to be easy to comprehend, so we use a different
			 * pattern.
			 */
			int number; // street number retrieved from the database
			boolean failure = false;
			if (!rs.next()) {
				failure = true;
				reportFailure("No rows in ResultSet");
			}
			if ((number = rs.getInt(1)) != 300) {
				failure = true;
				reportFailure("Wrong row returned, expected num=300, got "
						+ number);
			}
			if (!rs.next()) {
				failure = true;
				reportFailure("Too few rows");
			}
			if ((number = rs.getInt(1)) != 1910) {
				failure = true;
				reportFailure("Wrong row returned, expected num=1910, got "
						+ number);
			}
			if (rs.next()) {
				failure = true;
				reportFailure("Too many rows");
			}
			if (!failure) {
				System.out.println("Verified the rows");
			}
			// delete the table
			s.execute("drop table location");
			System.out.println("Dropped table location");
			/*
			 * We commit the transaction. Any changes will be persisted to the
			 * database now.
			 */
			conn.commit();
			System.out.println("Committed the transaction");
			/*
			 * In embedded mode, an application should shut down the database.
			 * If the application fails to shut down the database, Derby will
			 * not perform a checkpoint when the JVM shuts down. This means that
			 * it will take longer to boot (connect to) the database the next
			 * time, because Derby needs to perform a recovery operation.
			 * 
			 * It is also possible to shut down the Derby system/engine, which
			 * automatically shuts down all booted databases.
			 * 
			 * Explicitly shutting down the database or the Derby engine with
			 * the connection URL is preferred. This style of shutdown will
			 * always throw an SQLException.
			 * 
			 * Not shutting down when in a client environment, see method
			 * Javadoc.
			 */
			if (framework.equals("embedded")) {
				try {
					// the shutdown=true attribute shuts down Derby
					DriverManager.getConnection("jdbc:derby:;shutdown=true");
					// To shut down a specific database only, but keep the
					// engine running (for example for connecting to other
					// databases), specify a database in the connection URL:
					// DriverManager.getConnection("jdbc:derby:" + dbName +
					// ";shutdown=true");
				} catch (SQLException se) {
					if (((se.getErrorCode() == 50000) && ("XJ015".equals(se
							.getSQLState())))) {
						// we got the expected exception
						System.out.println("Derby shut down normally");
						// Note that for single database shutdown, the expected
						// SQL state is "08006", and the error code is 45000.
					} else {
						// if the error code or SQLState is different, we have
						// an unexpected exception (shutdown failed)
						System.err.println("Derby did not shut down normally");
						printSQLException(se);
					}
				}
			}
		} catch (SQLException sqle) {
			printSQLException(sqle);
		} finally {
			// release all open resources to avoid unnecessary memory usage
			// ResultSet
			try {
				if (rs != null) {
					rs.close();
					rs = null;
				}
			} catch (SQLException sqle) {
				printSQLException(sqle);
			}
			// Statements and PreparedStatements
			int i = 0;
			while (!statements.isEmpty()) {
				// PreparedStatement extend Statement
				Statement st = (Statement) statements.remove(i);
				try {
					if (st != null) {
						st.close();
						st = null;
					}
				} catch (SQLException sqle) {
					printSQLException(sqle);
				}
			}
			// Connection
			try {
				if (conn != null) {
					conn.close();
					conn = null;
				}
			} catch (SQLException sqle) {
				printSQLException(sqle);
			}
		}
	}

	/**
	 * Reports a data verification failure to System.err with the given message.
	 *
	 * @param message
	 *            A message describing what failed.
	 */
	private void reportFailure(String message) {
		System.err.println("\nData verification failed:");
		System.err.println('\t' + message);
	}

	/**
	 * Prints details of an SQLException chain to <code>System.err</code>.
	 * Details included are SQL State, Error code, Exception message.
	 *
	 * @param e
	 *            the SQLException from which to print details.
	 */
	public static void printSQLException(SQLException e) {
		// Unwraps the entire exception chain to unveil the real cause of the
		// Exception.
		while (e != null) {
			System.err.println("\n----- SQLException -----");
			System.err.println("  SQL State:  " + e.getSQLState());
			System.err.println("  Error Code: " + e.getErrorCode());
			System.err.println("  Message:    " + e.getMessage());
			// for stack traces, refer to derby.log or uncomment this:
			// e.printStackTrace(System.err);
			e = e.getNextException();
		}
	}

	/**
	 * Parses the arguments given and sets the values of this class's instance
	 * variables accordingly - that is, which framework to use, the name of the
	 * JDBC driver class, and which connection protocol to use. The protocol
	 * should be used as part of the JDBC URL when connecting to Derby.
	 * <p>
	 * If the argument is "embedded" or invalid, this method will not change
	 * anything, meaning that the default values will be used.
	 * </p>
	 * <p>
	 * 
	 * @param args
	 *            JDBC connection framework, either "embedded" or "derbyclient".
	 *            Only the first argument will be considered, the rest will be
	 *            ignored.
	 */
	private void parseArguments(String[] args) {
		if (args.length > 0) {
			if (args[0].equalsIgnoreCase("derbyclient")) {
				framework = "derbyclient";
				protocol = "jdbc:derby://localhost:1527/";
			}
		}
	}
}
